Urban heat island intensity (UHII) in Kolkata has been assessed using simplified numerical model for vertical temperature measurement in tropical monsoon summer month (June, 2015) during pre-onset of monsoon season. The data of 25 field observation sites show that the surface temperature curves are likely to mathematical trapeziums, and surface temperatures are related to vertical air temperatures. Therefore, approximated temperature trapeziums that are determined by high and lower air temperatures can be used to numerical simulation the vertical surface temperature fluctuation or variation. Two different field observation sites respectively in the urban and suburban areas were taken as model purpose. Distinct and good agreement was obtained between numerical simulation and observed temperature. Observed temperatures indicate the mean temperature under urban concrete surface environment is about 3.54 °C greater than that of adjacent suburban open surface. The deviation from normal is due to the heat wave environmental effect and different surface thermal effect, which are about 2.08 °C and 2.92 °C, respectively. Combined with air relative humidity (RH), ‘Heat’ islands associated with ‘Dry’ island, which means urban air relative humidity is lower than suburban air relative humidity (79.52 %,). According to the variation of RH and temperature deviation graphs, urban heat island, vertical surface types and rainfall are important factors that influence the air humidity and temperature.